The present invention relates to the use of parabolic reflectors in an antenna system for use in broadband satellite communications. More specifically, the invention relates to an antenna array of parabolic rectangular reflectors having a low profile suitable for mounting on an aircraft.
In the field of satellite communications, antenna systems for satellite communication are required to have a broad bandwidth while having a narrow antenna beam width. The broad bandwidth enables the antenna system to both transmit and receive signals over frequency bands of several GHz. The narrow antenna beam width provides a high gain for signals that are received and transmitted over a particular frequency to and from a particular satellite, and provides discrimination between satellites.
Although the antenna beam width is usually focussed on a particular satellite, it may also be necessary to alter the focus of the antenna beam toward another satellite.
Due to the high speed at which aircraft travel, antenna systems which are mounted on aircraft are required to maintain a low profile. The low profile minimizes drag. Typically, an antenna system is placed within a radome that has a height restriction in the range of 4 inches to 12 inches depending on the application type of aircraft.
Single parabolic reflectors are not ideal for use in applications requiring a low profile. This is due in part to the fact that a parabolic reflector has a low aspect ratioxe2x80x94it is difficult to optimally illuminate the entire reflector surface when the ratio of the aperture width to height is large. In order to illuminate the entire surface of the parabolic reflector, the reflector itself must be distanced from the reflector feed. For example, a parabolic reflector having a surface width of 28 inches would typically require the feed to be placed at least 10 inches from the reflector. This is well beyond the height restriction of the radome on an aircraft. Regardless of whether the feed is axial or offset, inside the radome, the geometry of a single parabolic reflector is less than ideal for use on an aircraft fuselage.
U.S. Pat. No. 5,929,819, issued to Grinberg, discloses a low profile antenna for satellite communications. Grinberg teaches the use of an array of antenna lenses for focussing guided and unguided waves to and from conventional antenna elements such as reflectors. Essentially, a number of antenna lenses are mounted overhead a corresponding number of antenna elements. Unfortunately, Grinberg would be impractical for placement inside a radome where height restrictions are a constraining factor.
In order to overcome the above shortcomings, the present invention seeks to provide an antenna system where a number of parabolic reflectors are contiguously disposed in a linear array. The antenna system would be small enough to fit within a radome, such that the physical dimensions and profile would minimally affect the drag on the aircraft. Furthermore, the antenna system seeks to provide high gain and a narrow beam width to support high data rates and provide adjacent satellite discrimination.
The present invention seeks to provide an antenna system consisting of parabolic rectangular reflectors disposed contiguously in a linear array. The use of parabolic rectangular reflectors permits the entire composite rectangular aperture to be excited without gaps in illumination. The parabolic rectangular reflectors permit a lower profile which is ideal for use on an aircraft. Each parabolic rectangular reflector has its own feed system and each of the feeds are excited in phase. The combined radiation patterns of the parabolic reflectors produce a beam with a narrow width. This narrow beamwidth permits the system to communicate with one source while filtering out signals coming from other sources. In one embodiment, the antenna system may be mechanically steered in order to communicate with a transmitter and/or receiver whose relative position is continuously varying with respect to the antenna system.
In one aspect, the present invention provides an antenna system including:
a common aperture surface;
at least two parabolic rectangular reflectors, each parabolic rectangular reflector having a concave surface, a long side and a short side providing a rectangular aperture, each parabolic rectangular reflector being disposed contiguously in a linear array defined by a linear axis forming a larger common rectangular aperture without gaps in illumination, each of the at least two parabolic rectangular reflectors having a corresponding reflector feed and the concave side of each of the at least two parabolic rectangular reflectors facing the reflector feed; and
a power splitting and combining means for feeding input power to each reflector feed;
wherein each of the at least two parabolic rectangular reflectors is supported by the common surface between the at least two parabolic rectangular reflectors and the corresponding reflector feeds and wherein the long side of each parabolic rectangular reflector is parallel to the linear axis of the linear array.